Abstract
Purpose: :
The pathology of glaucoma is characterized by loss of retinal ganglion cells (RGC) and is typically accompanied by sensitivity to intraocular pressure (IOP). RGC death in glaucoma is known to involve the mitochondrial–dependent apoptotic pathway. To assess the contribution of the FasL mediated pathway of apoptosis, we examined the expression and localization of FasL and its receptor, CD95, in the DBA/2 mouse model of glaucoma.
Methods: :
Retina were obtained from age–matched mice with low or high intraocular pressure as determined by tonopen measurement and examined gene expression, protein content and localization. For gene expression, cDNA was synthesized from harvested RNA and probed by reverse transcriptase PCR (RT–PCR). For protein expression, samples were analyzed by Western blot. For protein localization, cryostat sections were prepared from animals and analyzed by immunocytochemistry and in situ hybridization using standard protocols. To isolate the effects of pressure on FasL and CD95 in vitro, we created purified primary cultures of rat RGCs from post–natal rat retina. We then exposed these cultures to elevated hydrostatic pressure for 24 hours and probed by RT–PCR.
Results: :
RT–PCR and Western blot results demonstrate that CD95 and FasL are present in retina isolated from age–matched animals with low and high IOP. Age and IOP appear to modulate gene and protein expression of CD95 and FasL in a complex manner that we are pursuing further. In cryostat sections, CD95 and FasL were analyzed for their localization in vivo. FasL was found in glial cells, heavily concentrated in the extracellular space of RGCs, and intravascularly. Membrane bound CD95 was found in neurons of the inner nuclear layer and RGC layer. Interestingly, while CD95 levels decrease within the vasculature as a function of time and pressure, the expression levels in RGCs maintained in vitro increase.
Conclusions: :
CD95 and FasL are expressed and localized to a variety of retinal cells including neurons. CD95 is expressed in RGCs and responds to the effects of time and increased pressure, important glaucoma risk factors. FasL is expressed in the extracellular space around RGCs suggesting that FasL and CD95 may play an apoptotic role in glaucoma. The complex manner by which these binding partners interact suggests a role for FasL–mediated cell signaling in aged RGCs stressed by elevated IOP. The presence and upregulation of CD95 and FasL suggest the death receptor mediated apoptotic pathway is present and functions in RGCs and opens other avenues of possible therapeutics in treating glaucoma.
Keywords: cytokines/chemokines • apoptosis/cell death • degenerations/dystrophies